This invention relates to the structure and assembly of rechargeable lithium batteries from rechargeable lithium battery cells.
Rechargeable lithium battery cells are generally packaged as individual cell units in either cylindrical metal tubes or foil pouches. Each cell unit contains positive and negative electrodes, electrolyte and positive and negative current collectors. The current collectors must be accessible from outside of the package to enable electrical connection thereto.
Because of the materials used in a rechargeable lithium battery cell, the cell must be protected against moisture and oxygen ingress to avoid undesirable reactions. Furthermore, where liquid electrolytes are used, the packaging must also be capable of preventing liquid electrolyte egress. Cell seals are typically bulky and heavy, often representing in excess of 10% of cell weight and volume.
In order to meet various reserve capacity and voltage requirements, a plurality of lithium battery cells are typically enclosed in a plastic battery box with appropriate cell interconnections therebetween. The battery boxes primarily provide a structure for housing the battery cells. As the cells are themselves sealed against oxygen and moisture ingress and liquid electrolyte egress, it has not been found necessary or cost efficient in the past to provide a hermetically sealed battery box for lithium-ion cells.
In xe2x80x9cfoilxe2x80x9d pouch packaged lithium battery cells, the use of a polymeric coated foil gives rise to a need to adequately ensure that leads from the current collectors don""t contact the foil material and thereby xe2x80x9cshort-outxe2x80x9d. This problem is particularly acute along the outer edges of the foil covering which have usually been cut to size, thereby exposing the electrically conductive foil in close proximity to the leads, creating a need for shielding of the leads in this area.
It is an object of the present invention to provide a battery box for rechargeable lithium battery cells which is mechanically strong and hermetically sealable.
It is a further object of the present invention to provide a method for combining rechargeable lithium battery cells with a battery box enabling the elimination of foil encapsulation of individual cells and allowing thinner encapsulating materials.
A battery box sealable against moisture and oxygen ingress and liquid electrolyte egress. The battery box includes a first end, a second end opposite the first end, and side walls extending between the first and second ends to define a chamber for housing a number of rechargeable lithium battery cells.
The first end and the side walls are metallic and have a substantially moisture and oxygen gas impervious joint between them.
The second end is of a metal plastic laminate joinable to the side walls by a joining medium to form a substantially moisture and oxygen impervious joint therebetween. The second end has electrical connectors extending through it which enable substantially moisture and gas impervious connection to be made between current collectors of the rechargeable lithium battery cells and the outside of the battery box.
A method is provided for assembling a lithium battery from rechargeable lithium battery cell units which have positive and negative electrodes, an electrolyte and positive and negative current collectors. The method comprises the steps of:
Stacking a plurality of the cell units in a hermetically sealable box.
1. Providing an electrically insulating barrier between adjacent of the cell units and between the cell units and the box.
2. Making any desired electrical connections between selected of the positive and negative current collectors.
3. Providing electrical continuity between selected of the current collectors and an exterior of the battery box.
4. Hermetically sealing the battery box.